docs: def by_symbol(symbol, country_code=None):
      """Get list of possible currencies for symbol; filter by country_code
  
      Look for all currencies that use the `symbol`. If there are currencies used
      in the country of `country_code`, return only those; otherwise return all
      found currencies.
  
      Parameters:
          symbol: unicode                  Currency symbol.
          country_code: Optional[unicode]  Iso3166 alpha2 country code.
  
      Returns:
          List[Currency]: Currency objects for `symbol`; filter by country_code.
      """
      res = _data()['symbol'].get(symbol)
      if res:
          tmp_res = []
          for d in res:
              if country_code in d.countries:
                  tmp_res += [d]
  
          if tmp_res:
              return tmp_res
          if country_code is None:
              return res